Allylation intramolecular variant

The ene reaction as a reaction principle has been first recognized and systematically investigated by Alder It is a thermal addition reaction of a double bond species 2—the enophile—and an alkene 1—the ene—that has at least one allylic hydrogen. The intramolecular variant is of greater synthetic importance than is the intermolecular reaction. 

An intramolecular variant of the above chemistry has been used for the preparation of pyrroloindolizines. A -Allyl- and iV-propargyl-glyoxals react with tetrahydroisoquinoline to give 231 and 232, respectively (Equations 28 and 29). Furthermore, these reagents have been linked through the (V-substituent to a polymeric resin for further use in solid-phase and combinatorial chemistry <1997JA6153>. 

A mild one-pot procedure based on a platinum-catalyzed diborylation of 1,3-butadienes (see Eq. 30) gives doubly allylic boronate 144, which adds to an aldehyde to form a quaternary carbon center in the intermediate 145 (Eq. 105). The use of a tartrate auxiliary in this process leads to good levels of enantiose-lectivity in the final diol product, which is obtained after oxidation of the primary alkylboronate intermediate. Although examples of aliphatic, aromatic, and unsaturated aldehydes have been described, enantioselectivities vary widely (33 to 74% ee), and are good only for aliphatic aldehydes. An intramolecular variant of this interesting tandem reaction is also known. ... 

Similarly, an intramolecular variant utilizing carbamates 26 derived from allylic alcohols has been developed using an amine like Hunigs base (ethyl diisopropylamine) as additive [21], The products were obtained with complete regio- and diastereocontrol, but surprisingly, only in racemic form when chiral ligands like (DHQ PHAL, being established for the AA, were employed. 

Rh2(55-mepy)4] is particularly useful for intramolecular cyclopropanation in several examples up to 94% ee was obtained. [17] Highly substituted cyclopropanes are accessible by this reaction an example is given in Equation (b). With the two enantiomeric catalysts both enantiomeric products can be obtained from the same allyl diazoacetate. For this intramolecular variant the (Z) configuration of the olefin proves superior to the (E) configuration. 

Robertson and co-workers have investigated a TVpe II intramolecular version of the ene reaction in which the reacting partners, an olefin possessing an allylic hydrogen and an aldehyde, are tethered at an internal site [121]. In analogy with intramolecular variants in which the reactants are linked through an all-carbon tether [122], this reaction was antic-... 

Diels-Alder reactions. Compounds that give an oxygen-stabilized allyl cation are super-dienophiles in the presence of LiClQ,.OEt2. The method obviates the difficulties experienced with the low reactivities of 2-cyclohexenones. An intramolecular variant serves to construct tricyclic ketones expediently. 

A neat synthesis of a- and /S-panasinsene (255) has been described which incorporates an intramolecular variant of the cuprous triflate-catalysed photocycloaddition of the allylic alcohol (253) to afford (254).Oxidation of (254), followed by treatment with methyl-lithium and dehydration yielded a mixture... 

A modern variant is the intramolecular magnesium-ene reaction, e.g. the reaction of the alkene-allylic-Grignard compound 9 to give the five-membered ring product 10. This reaction proceeds regio- and stereoselectively, and is a key step in a synthesis of the sesquiterpenoid 6-protoilludene ... 

The first total synthesis of (+)-stenine has been accomplished in the laboratory of D.J. Hart/ The key steps were an intramolecular DIels-Alder reaction, an amidine variant of the Curtius rearrangement, an Eschenmoser-Clalsen rearrangement, a halolactonization, and a Keck allylation. The allylic alcohol precursor and A/,A/-dimethylacetamide dimethyl acetal was heated to reflux in xylenes for 4h to afford the desired amide in 93% isolated yield. The transition state most likely adopted a boatlike conformation. 

The comparison of intramolecular carbopalladation reactions of allenes and alkenes outlined in Schemes 9-5 and 9-6 illustrates that not every transition metal catalyzed ring closure necessarily involves a template effect. Others, however, clearly benefit from it. A prototype example is the palladium catalyzed cycloisomerization of alkenyl epoxides carrying distal pre-nucleophiles [38, 39], representing one variant of the famous Tsuji-Trost allylation [40]. 

Variants of the Michael addition include the allylation of cyclopropenone acetals and the intramolecular Stetter reaction. So far, only moderate enantioselectivity for the latter reaction has been achieved. (Note that the same chiral catalyst is useful for benzoin condensation. )... 

Harmata studied several variants of the intramolecular [4+3] cycloaddition including the cycloaddition of a furan tethered to an oxyallyl cation (Eq. 40), the latter generated through a clever TiCl4 initiated heterolysis of an allylic sulfone. This approach very nicely circumvents problems of performing intramolecular [4+3] cycloadditions based on a,a -dibromoketones as the allyl cation sources. 

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